KDE 4.2.4 is now in jaunty-backports and will be removed from the PPA shortly. Even if you have the PPA packages, please upgrade to the versions in jaunty-backports. There are several security fixes included in jaunty-backports that were not in the PPA packages.
Backports is not enabled by default, but is included in the standard /etc/apt/sources.list. You may need to enable it. The repository you want to enable looks like:
deb-src http://archive.ubuntu.com/ubuntu/ jaunty-backports main restricted universe multiverse

The sixth alpha for Kubuntu Karmic has been released. This release contains some notable changes to the boot system and should be treated with caution. See the release notes for more information and where to download.